The Detroit Auto Show traditionally belongs to the domestic automakers, who pull out all the stops as they unveil some of their best and brightest new products and concepts. This year, however, the ultimate showstopper may well be located at the Rolls-Royce display. The fabled British marque (now owned by BMW, of course) has chosen Detroit to reveal the 2008 Phantom Drophead Coupé, a jaw-droppingly spectacular 4-seat convertible aimed squarely at Bentley's Azure